C O M P L E X S Y S T E M S A N D B I O M E D I C A L S C I E N C E S

S C I E N T I F I C H I G H L I G H T S

6 0 H I G H L I G H T S 2 0 2 2 I

PRINCIPAL PUBLICATION AND AUTHORS

Low efficiency of laser heating of gold particles at the plasmon resonance - an X-ray calorimetry study, A. Plech (a), A.R. Ziefuss (b), M. Levantino (c), R. Streubel (b), S. Reich (a), S. Reichenberger (b), ACS Photon. 9, 2981-2990 (2022); https:/doi.org/10.1021/acsphotonics.2c00588 In situ structural kinetics of picosecond laser-induced heating and fragmentation of colloidal gold spheres, A. Ziefuß (b), S. Reich (a), S. Reichenberger (b), M. Levantino (c), A. Plech (a), Phys. Chem. Chem. Phys. 22, 4993-5001 (2020); https:/doi.org/10.1039/C9CP05202J (a) Institute for Photon Science and Synchrotron Radiation, Karlsruhe Institute of Technology, Karlsruhe (Germany) (b) Technical Chemistry and CENIDE, University Duisburg-Essen (Germany) (c) ESRF

REFERENCES

[1] V. Amendola, M. Meneghetti, Phys. Chem. Chem. Phys. 15, 3027-3046 (2013). [2] A.R. Ziefuss et al., Adv. Mat. 2101549 (2021).

due to the interaction of the near-field with the nanoscale environment. The study will enhance general understanding of how ultra-short laser pulses and

nanoparticles interact and how this interaction can be used to tune the properties of nanoparticles for future applications.

The general excitement born out of the ability to access the ultrafast time scales has caused a rush of new ideas, new materials and new instruments. There is clear evidence now that materials can be directed between different macroscopic states by using electronic or phononic excitations. One feat in particular has attracted a lot of effort, namely the control of materials with an ultrashort laser pulse, on pathways unattainable at thermodynamic equilibrium. Recent studies utilising time-resolved optical spectroscopy [1] revealed a size-dependent spin-state switching time and sparked the expectation that transition-metal compounds would obey the rule the smaller the faster , owing to a positive elastic feedback from the expanding lattice on the volume-changing molecules. At equilibrium, both the unit cell volume and the concentration of high spin molecules show correlated jumps upon the phase transition from low- to high-spin state at 165 K.

In this work, 100-ps X-ray diffraction was synchronised to a 1-ps pump laser exciting a charge transfer state to probe the photo-induced dynamics of an Fe(III) compound. The experiments were performed at beamline ID09 in quasi-grazing reflection geometry at 0.2° incidence angle to enhance the signal from the thin film sample and reduce diffuse background from a bulky substrate (Figure 50).

A quantitative structural analysis [2,3] at several time delays allowed to establish a sequence of events in the non-equilibrium dynamics. Interestingly, this material exhibits a very different behaviour from the insulator- to-metal transformation dynamics of an inorganic semiconductor upon propagation of laser-induced, long- range deformations [4]. In the latter case, the phase

Temporal decoupling between lattice expansion and molecular spin transition observed with time- resolved X-ray diffraction

Time-resolved X-ray diffraction was used to investigate the photo-induced dynamics in microcrystals of a spin crossover iron complex. By tracking the molecular spin state and the structure of the lattice after laser photo-excitation, it is demonstrated that the volume expansion precedes the thermo-elastic spin transition in this prototypical system for molecular cooperativity.